A radial piston pump for pumping water generally comprises a pump housing, a central drive mechanism and a surrounding pumping mechanism which has a plurality of radially oriented piston-and-cylinder units distributed around its circumference. The inlet and outlet valves for the individual cylinder chambers are positioned in the vicinity of the piston-and-cylinder units. Particularly these pumps are high pressure pumps. "Pure water" here means water without added lubricating agents.
In the conventional radial piston pump of the described type and for the described purpose, the drive mechanism runs in the water to be pumped or fed. That has proven satisfactory when the water to be pumped contains a lubricant in sufficient quantities, e.g. a lubricant/water emulsion containing water with about 5% lubricant.
With decreasing lubricant content of the water to be pumped one observes, especially at higher pumping speeds, increasing heat generation and a troublesome heating of the drive mechanism and the entire pump housing. The water containing the lubricant is an environmental contaminant when disposed of after use.